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New Zealand Engineering 1999 March Food All the World's a Stage - That which you take for granted, will eventually trip you up It is hard to imagine a more ho-hum facet to food process engineering than designing platforms. Most of the process design effort goes instead into optimising machinery, to manufacture the food product to its tight specification; pipes, wiring and platforms are often afterthoughts, abdicated to draftsmen and structural engineers. But consider this: On a square metre basis, even the gruesomely cheapest platform or mezzanine will cost more than the building in which it is placed. It will be so intimately intertwined with the plant and services that to replace it later will cost typically five times its original cost, and, for the same reason, in situ rejuvenation will prove impracticable. Yet if its shortcomings are serious enough, you may eventually be forced to do just that, as accidents and access problems become intolerable, hygiene fails, or as corrosion destroys its structure. In the worst scenario, trash will accumulate in uncleanable recesses, fester into a stinking bacterial sauce and drool out from the most unlikely places, into the food being processed beneath. Customers may become sick or even die, forcing product recall, lawsuits, bankruptcy and apocalyptic doom. You only get one chance to build it right; haste is fatal. English fails to offer a word for Levitology; the art of structurally supporting machines in a functional vertical relationship and providing access for services and human operators to tend them. The word "platform" conjures up precisely the wrong, simplistic image, so instead I will call this a "stage". In order to design this stage for high culinary drama, you must first generate its spatial definition. The fruit of this pre-design labour will be the simple elegance from which flow hygiene, longevity and cheapness. Act one, Scene
One: Lost in space Now you have created two series of levels: one for the people to stand on; and one for plant to stand on. Happiness is where these two requirements coincide. The fatal mistake is to call the job finished, making platforms at the various levels for the machines to stand on and numerous extra stands for the operators to use. Every step in level requires extra safety handrails and steps, to access structural deck levels irrelevant to plant operation. The whole deck system has to be larger to accommodate tortuous traffic paths, all resulting in an obstructive hotchpotch of expensive, irrelevant metal. Be bold, chop legs off machines or lengthen them if necessary; move drives, controls, valve manifolds and hatches; to force machine and people levels to coincide wherever possible. Take features such as control valve sets off machines altogether and relocate them outside the hygiene envelope, into the building roof space. Raise plant higher to get still more levels to coincide and if 2.1 metres clearance can be achieved, you can safely cross foot traffic paths underneath machines. Your process line elevation will climb like the ascent of Everest; for machines, tanks and hoppers usually obey the law of gravity, feeding in at the top and out at the bottom. If your building is cramped for space but has plenty of headroom, you might leave it at that, otherwise you must break the line at strategic places, pulling it back down to floor level and inserting elevators to replace gravity. This will give you a sawtooth shaped elevation. Resist the temptation to add too many elevators, they are expensive, wasteful, unreliable, and the lengthened line may challenge the floor area available. Next you have the option of providing a separate "stage" for each tooth of the saw, or bending the line back in a U turn, so that stages can be combined, for efficiency. After a week of hard work, all you have to show the boss are a few miserable horizontal lines and machines playing leap frog; in fact, the harder you have worked, the less you should have to show him. But believe me, a week of careful setout work is nothing compared to the waste and distress that follows haste. To mezzanine or not to mezzanine? That is the question. You may make the stage exactly as you have developed it, or if it is too tall or large, it may be better to insert a mezzanine floor at a strategic height to break it into smaller, more manageable pieces. As well as breaking the stage into small sub-systems, a mezzanine’s uniform grid structure makes it easier to set out plant below, and shields it from the process above. Future layout changes are more easily accommodated. Per square metre, a mezzanine is cheap, but it is not a complete system and only supplements staging, rather than replacing it. Large or small, stage design principles are the same, starting with a basic, tailormade support for the raised plant only, without any decking. This will typically be a relatively heavy, seismically designed structure, with beams and legs specifically placed to "pick up" all of the support points (feet) of the raised plant, while dodging any plant installed on the floor beneath. It need not necessarily be all one structure, and sometimes may be avoided altogether by instead extending machine legs or providing pedestal bases. Next, the access decks, stairs and catwalks are added, ignoring structure, optimised purely for access needs. Finally, the two are married, using as little secondary structure as possible; in fact, using folded deck upstands and handrails as structural flanges and trusses decks can often become largely self-supporting. The end result should have no piece of metal anywhere that can’t emphatically justify its existence. Axioms of
digital technology The structure must be as open as possible so that access underneath is unimpaired. It is far better to bite the bullet and pay for large portal frame members than to use cross bracing, which is purgatory for the operators and can also frustrate later process changes. Decks must have clean undersides, to preserve the hygienic environment below. Obviously grating decks are a no-no, as the crud on the operators’ boots will scrape off and rain pestilence down onto the food below. Dirt will accumulate on any horizontal surfaces such as structural steel flanges, making the structure difficult to clean. Avoid this by folding special channel members with the bottom flange angled down 45 degrees, or use deep box shapes or RHS seal welded directly to the underside of the deck plates. Hollow members can collect contaminated water inside which can then leak out elsewhere onto food; if used they must be totally sealed, with welded end caps and no bolt holes permitted. Concrete structures built properly with flat precast panels, can present a clean underside and avoid all internal water-collecting voids. However, minor cracks usually develop that let water from above dribble through onto processes beneath; and drilling a few thousand anchor bolts to affix plant and services doesn’t help the situation. Applying a polyester floor topping is the standard cure, but is not always successful. By contrast, a metal floor system can be seal welded and any leaks directly repaired, and holes for pipes and cables can be water-proofed by adding seal welded upstands. The sweetest detailing can turn to vinegar when Messrs Higgledy and Piggledy add the services, usually as an afterthought, on a bad hair day. What use is a clean, tidy under-structure, when riddled with holes and festooned with a jungle gym of pipes, ducts and cables? It may be difficult to even see your pristine handiwork behind the fire sprinklers, drains, cold water, hot water, steam, condensate, compressed air, HP, soap and process pipes, cable trunks and ventilation ducting. Bang goes your IPENZ design award. Services must be accommodated at the outset, to get the spaghetti under control. A good technique is to provide in-built trunking to conceal as much as possible and steer them over the process systematically. You are already stuck with big ugly beams underneath your mezzanine or stage, so why not box them in and let the services hitch a lift inside? Weld a stainless steel tray under the beam, with removable side covers. Use side projecting fire sprinklers concealed inside the trunking, hang the lights from the underside, run the wash-down hose pipes down the columns. It is surprising how much can be re-routed into these ducts, and with careful design they can even become part of your ventilation air supply system. Make a grid of large holes in the webs of the structural beams, so that services branches can be passed neatly through them instead of looping down underneath like haemorrhoids. For stages without a regular grid structure, the
same principles apply, but being more open, they often lend themselves more to vertical
services clusters dropped at strategic points from the hygiene ceiling above. Never under
estimate the capacity of your attic to conceal the burgeoning acreage of services clobber;
if God had meant us to live in a maze of reticulation, noisy pumps and fans, he would
never have given us sandwich panels. Materials:
Hobson's Choice This is why paint technology advances have only resulted in larger, chewier paint flakes getting into food. Galvanising doesn’t generally flake, but again it may be compromised or fall victim to chemical attack by cleaning agents and food acids. Hot vegetable juices can strip steel bare in just two weeks. Once compromised, mild steel is impracticable to re-coat in situ and you are heading down the slippery slope to reconstruction. Stainless steel is the star performer, but, like Schwarzenegger, it comes at a high price. Attention to the minimising design process is important, to keep both materials and the welding to a minimum. Distortion is a curse, large decks are best avoided and deck joints should weld directly onto heavy structural members where possible to stop them from warping. For large structural members, I have found schedule 10 pipe to be more cost effective than RHS, which is expensive and limited in available sizes. Large aluminium structures are not cost effective, but may suit decks in dry areas. Aluminium is prone to similar chemical attack to galvanising, also being soft; it can gouge, shedding swarf into food. Concrete is cost effective for large, uniform structures such as mezzanines, where precasting can be maximised and boxing minimised. It can be designed free of unhygienic internal voids, and is good for noise and vibration containment. However, for complex stages, cost escalates, and it is very unforgiving when changes need to be made. Curing time can also cripple the construction programme. All the world’s a stage, as Shakespeare
said. God designed his as a sphere, with gravity in the middle, uncountable levels and all
the services draped loose around the outside. There’s no accounting for taste, is
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